Process for preparing chromium phyllosilicate clay catalysts

ABSTRACT

A process for preparing pillared chromium phyllosilicate clay α-olefin catalysts is disclosed. This process utilizes palygorskite and sepiolite clays. The pillaring of said clays comprise the steps of: (a) preparing a hydrolyzed first solution by dissolving a chromium salt and a base in water, heating said first solution to a temperature in the range of about 20° C. to about 100° C. while stirring continuously until the solution reaches a pH in the range of about 1.5 to about 2.5 and thereby producing a master batch; (b) diluting said master batch with water to produce a diluted second solution and heating said diluted second solution to produce a heated second solution; (c) adding a solid clay selected from the group consisting of sepiolites and palagorskites to said heated second solution, and continuing heating; (d) recovering said pillared chain silicate clay; (e) drying said pillared chain silicate clay to form first product.

This application is a continuation-in-part of application Ser. No.07/803,864 filed Dec. 9, 1991, now abandoned.

This invention relates to a process for forming clay catalysts that canbe used in a catalyst system for the polymerization of α-olefins. In oneaspect, the present invention relates to novel polymerization catalysts.In another aspect, the present invention relates to a process forpolymerizing α-olefins. In yet another aspect, this invention relates tonovel polymers of α-olefins.

BACKGROUND OF THE INVENTION

The preparation of pillared interlayer clay compositions by reacting asmectite-type clay with an aqueous solution of suitable polymericcationic hydroxy metal complexes of metals, such as aluminum, titanium,zirconium and chromium is known, as illustrated in U.S. Pat. Nos.4,665,045, 4,742,033, herein incorporated by reference. Further, U.S.Pat. No. 4,665,045, Pinnavaia et al. discloses that such pillaredinterlayed clay compositions that are prepared with chromium can be usedin olefin polymerization.

However, there is an ever present need to develop pillared interlayeredclays with new processes that result in different catalysts. Equallyimportant is the need to develop a process to produce efficient claycatalysts on a commercial scale. Further, a better understanding of theconsiderable diversity within this group of clays is needed such thatthe type of polymers produced can be explored for special or uniqueproperties.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a novel methodfor preparing catalyst compositions.

It is another object of this invention to provide a novel catalystcomposition well-adapted for the polymerization of α-olefins.

It is still a further object of this invention to provide an improvedprocess for the polymerization of α-olefins.

These and other objects of the present invention will become apparentfrom the disclosure and claims herein provided.

In accordance with the present invention, there is provided a novelmethod for preparing a new catalyst composition efficient for use in thepolymerization of α-olefins by preparing a pillared phyllosilicate claycomprising the following steps of:

(a) preparing a hydrolyzed first solution by dissolving a chromium saltand a base in water, heating said first solution to a temperature in therange of about 20° C. to about 100° C. while stirring continuously untilthe solution reaches a pH in the range of about 1.5 to about 2.5 andthereby producing a master batch;

(b) diluting said master batch with water to produce a diluted secondsolution and heating said diluted second solution to produce a heatedsecond solution;

(c) adding a solid phyllosilicate lay selected from the group consistingof dioctahedral and trioctahedral smectites to said heated secondsolution, and continuing heating;

(d) recovering said pillared phylloilicate clay; and

(e) drying said pillared phyllosilicate clay to form a first product.

In a further embodiment there is provided the activation of said claycomprising the following steps of:

(a) heating said first product at a temperature in the range of about150° C. to about 500° C. and for a time period in the range of about 30minutes to about 10 hours in an inert atmosphere;

(b) thereafter heating said first product at a temperature in the rangeof about 500° C. to about 900° C. and for a time period in the range ofabout 1 hour to about 50 hours in an oxidizing atmosphere and recoveringsaid catalyst composition.

In further accordance with the present invention, there is provided animproved method for the polymerization of α-olefins which results innovel polymer compositions and which comprises: contacting at least onemono-1-olefin having 2 to 8 carbon atoms per molecule with saidcatalyst; optionally copolymerizing with a conomomer having from about 3to about 8 carbon atoms per molecule; and optionally combining saidcatalyst with an organo-metal cocatalyst.

DETAILED DESCRIPTION

General Preparation of Chromium-Pillared Clays

The clays employed in the present invention are the dioctahedral andtrioctahedral smectites which have a platelet morphology containingextended sheets of silica tetrahedra and alumina octahedra (smectites)or sheets of silica tetrahedra and magnesia octahedra joined together.The natural abundance and commercial availability of clays make them aninexpensive alternative to more costly synthetic silicas presently usedfor olefin polymerization.

The method employed consists of considerable modifications to theprocess disclosed in Pinnavaia et al of U.S. Pat. No. 4,665,045. Onedifferentiating factor is that Pinnavaia is limited to “. . . an aqueousslurry of a layer lattice clay.” The present invention provides a novelprocess for preparing a pillared phyllosilicate clay; the first step ofwhich is preparing a hydrolyzed first solution by dissolving a chromiumsalt and a base in water, heating said first solution to a temperaturein the range of about 20° C. to about 100° C. while stirringcontinuously until the solution reaches a pH in the range of about 1.5to about 2.5 and thereby producing a master batch. The heatingaccomplishes in a reasonable time the hydrolytic polymerization ofchromium while the pH indicates when to stop heating so as to optimizethe concentration of the highly polyhydroxy chromium oligomers. Usingthe pH of said first solution to determine when heating Is sufficient isa novel method of accomplishing what is referred to in prior patents as“aging”. Preferably, the heating is conducted at a temperature of about90° C. while stirring continues until said first solution reaches a pHof about 2.3.

Said base is selected from the group consisting of sodium carbonate,ammonium carbonate, sodium hydroxide and ammonium hydroxide withpreference given to sodium carbonate. Said salt is selected from thegroup consisting of chromium nitrate and chromium acetate withpreference given to chromium nitrate.

The second step is diluting said master batch with water to produce adiluted second solution and heating said diluted second solution toproduce a heated second solution. It was discovered that achieving adiluted said master batch facilitates the goal of producing saidpillared phyllosilicate clay on a commercial scale.

Pinnavaia discloses the preparation of a clay slurry to be contactedwith a chromium solution. In accordance with the present invention, saidmaster batch containing chromium in solution is diluted and dry (i.e.powdered or free flowing) clay is added. When said pillaredphyllosilicate clay is prepared on a commercial scale the liquid volumerequired to slurry such quantities is too great to be viable. It isunexpected that by diluting said master batch in lieu of slurrying saidclay, the liquid volume required is reduced to less than one-fourth ofthat otherwise required.

The dilution step also provides a means whereby the chromium content ofthe final catalyst can be controlled. When known methods of preparingpillared phyllosilicate clays are used, the final clay product is highin chromium content; and when this product is utilized as apolymerization catalyst, an unacceptably high amount of Cr(VI) ispresent. Possible health hazards associated with Cr(VI) are diminishedwhen the initial chromium content is controlled via the method of thepresent invention.

Said dilution is carried out such that said first solution is diluted tothe ratio of about 0.5 ml H₂O to about 10 ml H₂O to about 1 ml masterbatch, with a preferred amount of H₂O being 4 mls H₂O to about 1 mlmaster batch. Said said second solution is heated to a temperature inthe range of about 20° C. to about 100° C. with a preferred heating atabout 90° C.

The third step comprises adding a solid clay selected from the groupconsisting of dioctahedral and trioctahedral smectites to said heatedsecond solution. The clay is added in solid form for the reasons set outsupra. The liquid volume of said second solution is in the range ofabout 1 ml to about 50 mls per gram of clay and contains an amount ofchromium in the range of about 0.001 grams to about 0.01 grams per ml ofsaid second solution, with a preferred volume of said second solutionbeing about 5 mls per gram of clay and containing about 0.002 grams ofchromium per ml of said second solution.

The novel pillared clay may be recovered by conventional methods wellknown to those skilled in the art. However, it is preferred that saidpillared phyllosilicate clay be washed and centrifuged with an initialseries of washes being conducted with H₂O and a secondary series ofwashes being conducted with an alcohol for the purpose of removingunbound H₂O before the final drying step and thereby minimizing thecollapse of the clay pore structure due to the surface tension of theH₂O during the drying process. This produces a first product which isthereafter dried using any method known to those of skill in the artsuch as oven or vacuum, or freeze drying. Other methods to remove waterinclude but are not limited to azeotrope drying or spray drying.

General Activation of Chromium-Pillared Clays

The dried chromium pillared clays can be activated to achieve a catalystsystem by performing the following steps which comprise:

(a) heating said first product at a temperature in the range of about150° C. to about 500° C. and for a time period in the range of about 30minutes to about 10 hours in an inert atmosphere, with a preferredtemperature of about 500° C. for a time period of about 1 hour;

(b) thereafter heating said first product at a temperature in the rangeof about 500° C. to about 900° C. and for a time period in the range ofabout 1 hour to about 50 hours in an oxidizing atmosphere and recoveringa second product, with a preferred temperature of about 650° C. for atime period of about 3 hours.

Optionally, the activation may further comprise cooling said secondproduct to a temperature in the range of about 300° C. to about 500° C.and for a time period in the range of about 1 minute to about 5 hours ina reducing atmosphere, with a preferred temperature of 350° C. for atime period of about 30 minutes. The optional heating accomplishes amore productive olefin polymerization catalyst than that which can bemade via one-step continuous heating.

General Polymerication Process Utilizing Novel Catalyst System

The polymerization process of the present invention requires that atleast one mono-1-olefin having 2 to 8 carbon atoms per molecule becontacted with said novel catalyst system. The olefin is selected fromthe group consisting of ethylene, propylene, 1-pentene, 1-hexene, and1-octene. Preferably said olefin is predominantly ethylene.

A comonomer may be copolymerized with ethylene to form an ethylenecopolymer. Said comonomer can be selected from the group consisting ofpropylene, 1-butene, 1-pentene, 1-hexene, and 1-octene. Preferredcopolymers are those of ethylene and 0.4 to 1 weight percent of acomonomer selected from C₄ to C₁₂ mono-1-olefins, most preferablyhexene.

Additionally, said novel catalyst system may be combined with anorgano-metal cocatalyst selected from the group consisting of:triethylaluminum, triethylboron, and diethylsilane. Preferred cocatalystis triethylaluminum.

EXAMPLES

The following examples have been provided merely to illustrate thepractice of the invention and should not be read as to limit the scopeof the invention or the appended claims in any way.

Tables 1-4 define the characteristics and chemical composition ofphylosilicate clays as they exist in nature, in pillared form, afteractivation, and as utilized as catalysts for polymerization.

TABLE 1 Phyllosilicate Clays Defined Surface Pore Clay CEC* Area VolumeType Source meq/100 g M²/g cm³/g Dioctahedral Smm Synthetic Mixed-layer135.0 120.0 .47 Montmorillonite, NL Industries Vol Volclay, Bentonite,HPM-20, 68.7 34 .15 Wyoming Che Cheto, Apache Co., Arizona 105.0 83.0.27 Non Nontronite, Grant Co., Washington 84.7 54.0 .15 TrioctahedralHca Hector, California 29.1 51.  .094 Sap Synthetic Saponite, NLIndustries 105.0 Ver Vermiculite, Llano, Texas 9.0 17. .38 Table 1presents data which characterizes the phyllosilicate clays utilized.*CEC = Cation Exchange Capacity

TABLE 2 Pillared Chromium Phyllosilicate Clays Surface Pore Area VolumeCatalyst Clay Type Cr. Wt. % M²/g cm³/g Dioctahedral A Smm 7.9 185 .55 BVol 11.7 296 .59 C Che 11.0 235 .18 D Non 10.0 269 .23 Trioctahedral EHca 22.0 Table 2 presents chemical and physical data which characterizesthe phyllosilicate clays after being chromium pillared. The surface areaand pore volume were determined by BET(N₂) method.

TABLE 3 Activated Pillared Clay Catalysts Surface Pore Activation AreaVolume Catalyst Clay Type Conditions Cr Wt. % M²/g cm³g Dioctahedral ASmm 500/N₂, 600/Air 10.0 103 .25 B Vol 500/N₂, 600/Air 15.0 117 .16 FChe 600/Air 17.0 130 .22 D Non 500/N₂, 600/Air 12.0 104 .10Trioctahedral G Hca 500/N₂, 600/Air 36.0 186 .28 J Sap 500/N₂, 600/Air11.0 240 .23 Table 3 presents chemical and physical data whichcharacterizes the clay catalysts made from phyllosilicate clays.

TABLE 4 Polymerizations CoReagents g Polymer/ Density Catalyst Clay Type(ppm) g Catalyst/hr HLMI*¹ g/cm³ Dioctahedral A Smm TEA(2)*² 1130  .02.950 B Vol TEA(2) 760 .01 .950 I Vol 602 .0  .950 H Vol TEA(2)/H₂*³ 534.11 .954 F Che TEA(2) 430 .01 .951 D Non TEA(2)  30 .01 Trioctahedral GHca TEA(2) 1020  .06 .950 J Sap TEA(2) 920 .03 K Ver TEA(2) 360 .06 .955Table 4 presents data which demonstrates polymerization resultsutilizing phyllosilicate clay. *¹HLMI — High Load Melt Index *²TEA —Triethylaluminum *³H₂ — Hydrogen

Preparation of Chromium-Smectite Dioctahedral Pillared Clay Example I

The clay used was the Wyoming bentonite, HPM-20, obtained from AmericanColloid Company. The analysis supplied by the vendor indicates thedioctahedral clay was comprised of the following compounds calculated inoxide form: 63.02 weight percent SiO₂; 21.08 weight percent Al₂O; 3.25weight percent Fe₂O₃ 0.35 weight percent FeO; 2.67 weight percent MgO;2.57 weight percent Na₂O; 0.65 weight percent CaO; 0.07 weight percentTiO; and 5.64 weight percent H₂O. The cation exchange capacity wasmeasured at 68.7 meq/100 grams. Nitrogen pore size distributionmeasurements showed a surface area of 34 m²/gram and a pore volume of0.15 cc/gram.

Preparation of Master Batch

Dissolved 1333 grams (3.33 moles) of Cr(NO₃)₃.9H₂O in 13.3 liters ofdeionized water to which was added slowly while stirring a solution madeby dissolving 353 grams (3.33 moles) of Na₂CO₃ in 6.7 liters ofdeionized water. While stirring continuously, the mixture was heated at90-95₂C for 15 to 24 hours replenishing any water lost because ofevaporation. The mixture was cooled and stored at ambient temperature.

Three-hundred and fifty ml of dionized water was heated to 90-95° C. Tothis hot solution was added 50 ml of master batch. After the 90-degreetemperature of the solution was reestablished, 20 grams of (bentonite)clay was added slowly while continually stirring. After the addition ofclay, stirring and heating of solution was continued for 90 minutes.After cooling to ambient temperature the mixture was transferred to a 1liter centrifuge bottle. The mixture was centrifuged and washed sixtimes with 500 ml portions of deionized water followed by four timeswith 500 ml portions of methanol. The pillared clay was dried in avacuum oven set at 52° C. with a nitrogen purge for 40 hours. The samplewas ground using a Laboratory mill (Janke & Kunkel KG, Type A10) andpassed through a No. 50 sieve to achieve Product V.

Activation Example II

Product V was activated for polymerization in a laboratory sizedfluidized bed (48 millimeters O.D. quartz tube) at elevated temperaturesby sequential treatment with a stream of dry nitrogen for one hour at500° C. followed by a stream of dry air for three hours at 650° C. Afteractivation, the catalyst was cooled under a stream of dry nitrogen toambient temperature, recovered and stored in dry nitrogen until readyfor use to produce Catalyst VI.

Example III

Activated in a similar manner to Al except after air oxidation, thecatalyst was cooled under nitrogen to 350° C. at which temperature astream of dry CO is passed through the catalyst bed for 30 to 45minutes. The CO was then purged with dry nitrogen while cooling toambient temperature. Catalyst was recovered and stored as above toproduce Catalyst V2.

Preparation of Chromium-Smectite Trioctahedral Pillared Clay Catalysts

An example of a smectite trioctahedral clay used, was the hectorite,Imvitone 38H, obtained from Industrial Mineral Ventures of Las Vegas,Nev.

Example IV

As described in Example I except used 20 grams of the hectorite clayinstead of the bentonite to achieve Product H.

Activation Example V

Product B was activated as described in Example II to produce CatalystH1.

Example VI

Product H was activated as described in Example III to produce CatalystH2.

Example VII

Product H was activated as in the manner described in Example II exceptProduct H was heated at 650° C. for four hours without the preparatorynitrogen step to produce Catalyst H3.

Polymerization Example VIII

The polymerization of ethylene alone or in admixture with hexene-1comonomer was carried out in a particle form process employing a 2.6liter stainless-steel jacketed reactor. After flushing the clean reactorwith dry nitrogen and dry isobutane vapor, one liter of dry, liquidisobutane was added as diluent. The sealed reactor was heated to thespecified temperature after which a weighted amount of catalyst (0.03 to1 gram) was charged and a solution of cocatalyst, if used, amounting toabout 1.0-2.0 mL of a 0.5 weight percent organometal compound such astriethylaluminum triethylboron and diethylsilane and mixture thereof.The reactor was then pressurized to 550 psig with ethylene andmaintained at that pressure throughout the reaction with ethylene flowbeing regulated by the rate of polymerization. Polymerization time wasnormally one hour. The productivity is calculated by dividing the weightof the dried reactor product by the weight of catalyst for a one-hourrun and is expressed in terms of grams per polymer per gram catalyst perhour. Polymerization times deviating from 60 minutes are normalized to60 minutes by assuming a linear polymerization response during the run.Thus, the uncorrected productivity value is corrected to 60 minutes bymultiplying it with 60 and dividing that result by the actualpolymerization time in minutes.

The catalyst, polymerization conditions, results and selected propertiesof the polyethylenes obtained are presented in Table 5.

TABLE 5 Polymerization Results and Polyethylene Properties PolymerProperties Catalyst Temp. Adjuvant Productivity Density No.(a) ° C.(ppm) g/g/hr HLMI g/cc V 95 TEA(5) 300 V 95 TEA(5) 400 0.02 H 95 TEA(5)1100  0.06 H 95 TEA(5) 780 0.27 H 95 TEA(5)  520* 0.23 0.946 H 95 TEA(5)650 *In the presence of 3 weight percent hexene-1

That which is claimed is:
 1. A process for preparing a pillaredphyllosilicate clay which comprises: (a) preparing a hydrolyzed firstsolution by dissolving a chromium salt and a base in water, heating saidfirst solution to a temperature in the range of about 20° C. to about100° C. while stirring continuously until the solution reaches a pH inthe range of about 1.5 to about 2.5 and thereby producing a masterbatch; (b) diluting said master batch with water to produce a dilutedsecond solution and heating said diluted second solution to produce aheated second solution; (c) adding a solid phyllosilicate clay selectedfrom the group consisting of dioctahedral and trioctahedral smectites tosaid heated second solution, and continuing heating; (d) recovering saidpillared phyllosilicate clay; and (e) drying said pillaredphyllosilicate clay to form a first product.
 2. A process according toclaim 1 wherein said base is selected from the group consisting ofsodium carbonate, ammonium carbonate, sodium hydroxide and ammoniumhydroxide.
 3. A process according to claim 1 wherein said base is sodiumcarbonate.
 4. A process according to claim 1 wherein said salt isselected from the group consisting of chromium nitrate and chromiumacetate.
 5. A process according to claim 1 wherein said salt is chromiumnitrate.
 6. A process according to claim 1 wherein said heating of saidfirst solution is conducted at a temperature of about 90° C. whilestirring continues until said first solution reaches a pH of about 2.3.7. A process according to claim 1 wherein said first solution is dilutedto the ratio in the range of about 0.5 ml H₂O to about 10 mls H₂O toabout 1 ml master batch.
 8. A process according to claim 1 wherein saidfirst solution is diluted to the ratio of about 4 mls H₂O to 1 mlmasterbatch.
 9. A process according to claim 1 wherein said secondsolution is heated to a temperature of about 90° C.
 10. A processaccording to claim 1 wherein said clay which is added to said secondsolution is a solid dioctahedral smectite.
 11. A process according toclaim 10 wherein the liquid volume of said second solution is in therange of about 1.0 mls to about 50 mls per gram of clay and contains anamount of chromium in the range of about 0.001 grams to about 0.01 gramsper ml of said second solution.
 12. A process according to claim 11wherein the liquid volume of said second solution is about 5 mls pergram of clay and contains about 0.002 grams of chromium per ml of saidsecond solution.
 13. A process according to claim 1 wherein said claywhich is added to said second solution is a solid trioctahedralsmectite.
 14. A process according to claim 13 wherein the liquid volumeof said second solution is in the range of about 1.0 mls to about 50 mlsper gram of clay and contains an amount of chromium in the range ofabout 0.001 to about 0.01 per ml of said second solution.
 15. A processaccording to claim 14 wherein said liquid volume of said second solutionis about 9 mls per gram of clay and contains about 0.0022 grams ofchromium per ml solution.
 16. A process according to claim 1 comprisingactivating said pillared phyllosilicate clay first product to produce acatalyst system wherein said activating comprises: (a) heating saidfirst product at a temperature in the range of about 150° C. to about550° C. and for a time period in the range of about 30 minutes to about10 hours in an inert atmosphere; (b) thereafter heating said firstproduct at a temperature in the range of about 500° C. to about 900° C.and for a time period in the range of about 1 hour to about 50 hours inan oxidizing atmosphere and recovering a second product.
 17. A processaccording to claim 16, further comprising cooling said second product toa temperature in the range of about 300° C. to about 500° C. and for atime period in the range of about 1 minute to about 5 hours in areducing atmosphere.
 18. A process in accordance with claim 17 whereinsaid second product is heated at a temperature of about 350° C. for atime period of about 30 minutes in a reducing atmosphere.
 19. A processin accordance with claim 16 wherein said first product is heated at atemperature in an inert atmosphere of about 500° C. for a time period ofabout 1 hour; and said first product is reheated at a temperature ofabout 650° C. for a time period of about 3 hours in an oxidizingatmosphere.
 20. A process for preparing a pillared phyllosilicate claywhich comprises: (a) preparing a hydrolyzed first solution by dissolvingchromium nitrate and sodium carbonate in water, heating said firstsolution to a temperature of about 90° C. while stirring continues untilsaid first solution reaches a pH of about 2.3 and thereby producing amaster batch; (b) diluting said master batch wish water to achieve aratio of about 4.0 mls H₂O to about 1 ml master batch to produce adiluted second solution and heating said diluted second solution at atemperature of about 90° C.; (c) adding solid dioctahedral smectite clayto said second solution in a ratio of about 5.0 mls of second solutionper gram of clay wherein said second solution contains 0.002 grams ofchromium; (d) recovering said pillared phyllosilicate clay to produce afirst product by washing and centrifuging said second solution andthereafter drying said first product.